In a liquid crystal display, a backlight which illuminates liquid crystal cells is used. Depending on the type of the liquid crystal display, an edge light type backlight is used in a liquid crystal monitor, while a direct type backlight is used in a liquid crystal television. As a reflection film for these backlights, a porous white film formed by air bubbles (JPA1996-262208) is conventionally used. Furthermore, a white film, in which ultraviolet absorbing layers are multilayered to prevent the film from turning yellow due to ultraviolet rays emitted from a cold cathode fluorescent lamp, is also proposed (JPA2001-166295 and JPA2002-90515).
Various methods for improving various characteristics of the luminance are disclosed for these reflection films. Examples of the disclosed methods are a method wherein a light shielding layer is provided on a surface of the film opposite to a light source to improve the luminance in the edge light type (JPA2002-333510), a method wherein a refractive index difference generated between a spherical particle and binder is selected to control light diffusion so that front face luminance by a light diffuser sheet is improved (JPA2001-324608), and a method wherein diffusion of a surface of the film on the light source side is controlled in a reflection sheet in the direct type backlight so that any Luminance Mura (an unevenness in the luminance) in the backlight is improved (JPA2005-173546).
In a reflection film for a liquid crystal television, which has been rapidly advancing, cost reduction is strongly demanded, while the improvement of reflection characteristics of the reflection film is even more strongly demanded than in the past because the number of expensive sheets used in an upper section of the light source can be reduced when the luminance of the backlight is improved as a result of the improvement of the reflection characteristics of the reflection film. For example, in one constitution of the backlight for the liquid crystal television, a diffuser plate (thickness of approximately 2 mm), a diffuser film (thickness of approximately 200 μm-300 μm), a diffuser film (thickness of approximately 200 μm-300 μm), and a diffuser film (thickness of approximately 200 μm-300 μm) are multilayered from the light source side in this order. When the luminance of the entire backlight is improved by 2-3%, one of the diffuser films will be reduced in the constitution.
However, the reflection characteristics of the reflection film, which largely depends on a void structure inside the white film, cannot be really any further improved by simply making appropriate modifications to the void structure.
In a manner different from conventional methods, it could be helpful to improve the luminance by making appropriate modifications to the surface of the white film on the light source side. More specifically, it could be helpful to provide a white reflection film which is capable of improving reflection characteristics and thereby contributing to the improvement of luminance of a backlight such that a particular coating layer is provided on at least one surface of the white film.